| 1. |
- Ahani, Ghafour, et al.
(författare)
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Age-Optimal UAV Scheduling for Data Collection With Battery Recharging
- 2021
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 25:4, s. 1254-1258
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Tidskriftsartikel (refereegranskat)abstract
- We study route scheduling of a UAV for data collection from sensor nodes (SNs) with battery recharging. The freshness of the collected information is captured by the metric of age of information (AoI). The objective is to minimize the average AoI cost of all SNs over a scheduling time horizon. We prove that the problem in its general form is NP-hard. Then, for a special case of the problem, we prove that optimum can be computed in polynomial time. Next, we develop an algorithm based on graph labeling. Finally, we show the effectiveness of our algorithm in comparison to greedy scheduling.
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| 2. |
- Braga Jr, Iran M., et al.
(författare)
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Joint Pilot and Data Power Control Optimization in the Uplink of User-Centric Cell-Free Systems
- 2022
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 26:2, s. 399-403
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Tidskriftsartikel (refereegranskat)abstract
- Joint pilot and data power control (JPDPC) is known to have a large impact on both the overall spectral/energy efficiency and fairness of cell-based systems. However, the impact of JPDPC on the inherent spectral/energy efficiency and fairness trade-off in cell-free (CF) systems is much less understood. In this letter, considering pilot contamination, user-centric clustering and multi-antenna access points, we formulate novel JPDPC problems in CF systems as distinct optimization tasks, whose objectives are maximizing the minimum spectral efficiency (SE), maximizing the total SE and maximizing the product of the individual signal-to-interference-plus-noise ratios. Since these problems are non-convex, we solve them by combining successive convex approximation and geometric programming. To the best of our knowledge, this is the first letter analyzing and optimizing JPDPC in user-centric CF systems. Our results indicate that JPDPC allows users to save more energy than the disjoint optimization of pilot and data powers when maximizing the minimum SE, while showing that JPDPC plays a crucial role in balancing between SE and fairness also in CF systems.
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| 3. |
- Braga Jr, Iran M., et al.
(författare)
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User Scheduling Based on Multi-Agent Deep Q-Learning for Robust Beamforming in Multicell MISO Systems
- 2020
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 24:12, s. 2809-2813
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Tidskriftsartikel (refereegranskat)abstract
- Maximizing the rate in multiple input single output (MISO) systems using distributed algorithms is an important task that typically incurs high computational cost. In this work, we propose two deep Q-learning-based user scheduling schemes to solve the beamforming problem of sum-rate maximization with per base station power constraints in multicell MISO scenarios. The two key features of the proposed algorithms are that they are executed in a distributed fashion and are robust with respect to channel state information (CSI) errors. Simulation results show that in the presence of CSI errors the proposed schemes outperform state-of-the-art algorithms both in terms of average spectral efficiency and execution time.
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| 4. |
- Chen, Zhengchuan, et al.
(författare)
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Age of Information of a Dual Queue Status Update System: A Stochastic Hybrid Systems Method
- 2023
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 27:7, s. 1714-1718
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Tidskriftsartikel (refereegranskat)abstract
- Using redundant devices to update the status can improve the robustness against transmission failure, thus improving timeliness of information. However, out of order update arrivals resulting from multiple devices impose a significant challenge to the analysis of timeliness of information in such systems. This letter studies the average age of information (AoI) of a dual queue status update system under zero-wait policy. We leverage tools from stochastic hybrid systems to derive closed-form expression for the average AoI of the dual queue system and extend the result to the three-queue system. The results show that the average AoI of the dual queue system can be reduced by 37.5% compared to that using only a single queue.
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| 5. |
- Chien, T. Van, et al.
(författare)
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Coverage Probability and Ergodic Capacity of Intelligent Reflecting Surface-Enhanced Communication Systems
- 2021
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Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 25:1, s. 69-73
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Tidskriftsartikel (refereegranskat)abstract
- This letter studies the performance of a single-input single-output (SISO) system enhanced by the assistance of an intelligent reflecting surface (IRS), which is equipped with a finite number of elements under Rayleigh fading channels. From the instantaneous channel capacity, we compute a closed-form expression of the coverage probability as a function of statistical channel information only. A scaling law of the coverage probability and the number of phase shifts is further obtained. The ergodic capacity is derived, then a simple upper bound to simplify matters of utilizing the symbolic functions and can be applied for a long period of time. Numerical results manifest the tightness and effectiveness of our closed-form expressions compared with Monte-Carlo simulations.
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| 6. |
- DAndrea, Carmen, et al.
(författare)
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Improving Cell-Free Massive MIMO by Local Per-Bit Soft Detection
- 2021
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 25:7, s. 2400-2404
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we consider the uplink of a cell-free Massive multiple-input multiple-output (MIMO) network where each user is decoded by a subset of access points (APs). An additional step is introduced in the cell-free Massive MIMO processing: each AP in the uplink locally implements soft MIMO detection and then shares the resulting bit log-likelihoods on the front-haul link. The decoding of the data is performed at the central processing unit (CPU), collecting the data from the APs. The non-linear processing at the APs consists of the approximate computation of the posterior density for each received data bit, exploiting only local channel state information. The proposed method offers good performance in terms of frame-error-rate and considerably lower complexity than the optimal maximum-likelihood demodulator.
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| 7. |
- Farooq, Muhammad Umar, et al.
(författare)
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Improving the Thresholds of Generalized LDPC Codes with Convolutional Code Constraints
- 2023
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 27:7, s. 1679-1683
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Tidskriftsartikel (refereegranskat)abstract
- CC-GLPDC codes are a class of generalized low-density parity-check (GLDPC) codes where the constraint nodes (CNs) represent convolutional codes. This allows for efficient decoding in the trellis with the forward-backward algorithm, and the strength of the component codes easily can be controlled by the encoder memory without changing the graph structure. In this letter, we extend the class of CC-GLDPC codes by introducing different types of irregularity at the CNs and investigating their effect on the BP and MAP decoding thresholds for the binary erasure channel (BEC). For the considered class of codes, an exhaustive grid search is performed to find the BP-optimized and MAP-optimized ensembles and compare their thresholds with the regular ensemble of the same design rate. The results show that irregularity can significantly improve the BP thresholds, whereas the thresholds of the MAP-optimized ensembles are only slightly different from the regular ensembles. Simulation results for the AWGN channel are presented as well and compared to the corresponding thresholds.
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| 8. |
- Farsaei, Amirashkan, et al.
(författare)
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Uniform Linear Arrays With Optimized Inter-Element Spacing for LOS Massive MIMO
- 2021
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 25:2, s. 613-616
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, a uniform linear array (ULA) is proposed for line-of-sight massive multiple-input-multiple-output (MIMO). It is assumed that the number of antennas is fixed. For a given ULA with an arbitrary inter-element spacing, the probability that the correlation among the channel vectors of two users being above a threshold value is derived. The inter-element spacing of the proposed ULA is the one for which the aforementioned probability is minimized. To show the effectiveness of the proposed ULA, simulation results for two scenarios are given for a 64-antenna ULA that serves 6 single-antenna users. By using the proposed ULA instead of conventional half-wavelength ULA, 5th percentile sum-rate for zero-forcing precoder is improved by 9.90 bits/channel use in first scenario without dropping, and by 1.43 bits/channel use in second scenario with dropping 1 user.
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| 9. |
- Fountoulakis, Emmanouil, et al.
(författare)
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Goal-Oriented Policies for Cost of Actuation Error Minimization in Wireless Autonomous Systems
- 2023
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 27:9, s. 2323-2327
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Tidskriftsartikel (refereegranskat)abstract
- We consider the minimization of the cost of actuation error under resource constraints for real-time tracking in wireless autonomous systems. A transmitter monitors the state of a discrete random process and sends updates to a receiver over an unreliable wireless channel. The receiver then takes actions according to the estimated state of the source. For each discrepancy between the real state of the source and the estimated one, we consider a different cost of actuation error. This models the case where some states, and consequently the corresponding actions to be taken, are more important than others. We provide two algorithms, a first one reaching an optimal solution but of high complexity, and a second low-complexity one that provides a suboptimal solution. Our simulation results evince that the performance of the two algorithms are quite close.
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| 10. |
- Huang, Huiping, 1991, et al.
(författare)
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Sparse Array Design for Dual-Function Radar-Communications System
- 2023
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 27:5, s. 1412-1416
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Tidskriftsartikel (refereegranskat)abstract
- The problem of sparse array design for dual-function radar-communications is investigated. Our goal is to design a sparse array which can simultaneously shape desired beam responses and serve multiple downlink users with the required signal-to-interference-plus-noise ratio levels. Besides, we also take into account the limitation of the radiated power by each antenna. The problem is formulated as a quadratically constrained quadratic program with a joint-sparsity-promoting regularization, which is NP-hard. The resulting problem is solved by the consensus alternating direction method of multipliers, which enjoys parallel implementation. Numerical simulations exhibit the effectiveness and superiority of the proposed method which leads to a more power-efficient solution.
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